This invention relates to fluoropolymer film structures and thermoformable laminates produced therefrom.
Fluoropolymer films have long been used as a protective and decorative overlay for a variety of substrates such as metal, wood, and thermoplastic and thermoset polymers. With its excellent chemical resistance and weathering properties, a thin layer of fluoropolymer film can protect less durable substrates from damage in both exterior and interior use. In recent years, manufacturers of automobiles, recreational vehicles, sports craft and industrial and farm equipment have begun using decorative fluoropolymer film structures to surface selected parts of vehicles and equipment in lieu of paint. Single layer polymer film and multilayer polymer films have been used. Especially useful is a laminate of a pigmented resin layer and a clear resin layer which simulates a base coat/clear coat paint appearance. Film structures of this type are often referred to as xe2x80x9cdry paintxe2x80x9d. The use of dry paint is desirable since it avoids the need for solvents associated with conventional paint finishes. Dry paint films and laminates are especially useful for thermoformed polymeric parts, especially those with surface contours which are difficult to paint. Further, a dry paint surface allows manufacturers to use lower cost plastic substrates, which are not usable if painted by conventional means because of the unacceptable aesthetic finish that results.
Fluoropolymer films such as polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF) polymers and copolymers and blends of acrylic polymers and PVDF are often used as the decorative surface for dry paint due to their exceptional outdoor durability, chemical resistance and thermoformability. In the manufacture of parts finished with dry paint films, the film or laminate is often applied to a thermoplastic substrate which is then subjected to a thermoforming operation. A wide number of thermoplastic substrates are desirable for use such as polyolefins, polyesters, nylon, ABS, etc. However, forming a secure bond between fluoropolymer and such substrates is difficult. A bond is needed that will not delaminate after years of outdoor exposure. A manufacturing system for laminates of fluoropolymer films and thermoplastic substrates is also needed which is versatile enough to accommodate a variety of different thermoplastic materials and has a minimum number of processing steps.
U.S. Pat. No. 3,133,854 to Simms discloses a laminate structure of polyvinyl fluoride film with a variety of substrates such as metal, cellulose, cement, glass and polyvinyl chloride. The polyvinyl fluoride film is prepared by chemically activating the surface and the laminate is formed by using an intermediate layer of amine functional acrylic copolymer. However, for some thermoplastic substrates, the bond formed between the PVF layer and the substrate is weak and unsatisfactory. There is no teaching in Simms of bonding polyvinyl fluoride to polyolefin, polyamide, or polyester substrates.
U.S. Pat. No. 5,139,878 to Kim et al. discloses multilayer film structures of fluoropolymer film and thermoplastic polymer films using an intermediate adhesive layer of alkyl ester copolymers, modified polyolefins, or blends thereof. Kim""s invention is aimed at producing packaging materials having good gas barrier properties and therefore the disclosure focuses on forming multilayer structures of chlorine containing fluoropolymer films adhered to polyester substrates. For some thermoplastic substrates and a number of fluoropolymer films, unsatisfactory bonds are formed using only the adhesive disclosed in this patent, especially if the laminate undergoes further forming steps.
Likewise, U.S. Pat. No. 4,585,694 to Dehennau describes multilayer structures of vinyl or vinylidene fluoride polymer and alpha-olefin polymer bonded by the joint aid of vinyl acetate polymer and a copolymer of ethylene and vinyl acetate. Laminate film structures of this type possess unsatisfactory bonds which are subject to delamination especially when further forming steps are performed. Further such bonds are considered unsuitable for long lived outdoor use.
In accordance with the present invention, a fluoropolymer film structure is provided which is particularly useful as a protective and decorative overlay for thermoplastic substrates. Employing a fluoropolymer film, the invention provides the attributes of outdoor durability, chemical resistance and thermoformability combined with paint-like aesthetics. The film structure includes at least one primer layer of amine functional polymer applied to one surface of the fluoropolymer film and at least one thermoplastic adhesive layer containing acid modified polyolefin adhered to the primed surface of the fluoropolymer film. The fluoropolymer film structure with primer and adhesive layers is advantageously used for lamination to any of a variety of thermoplastic substrates.
In a laminated film structure in accordance with the invention, the fluoropolymer film structure is adhered to the thermoplastic substrate. A secure bond forms between the fluoropolymer film structure and the thermoplastic substrate which resists delamination when exposed to moisture and humidity that attack adhesive bonds. Such laminated film structures can be produced by a simplified laminating process which decreases the heat and pressure requirements to secure a firm bond between the fluoropolymer film and a thermoplastic substrate.
Preferably, the acid modified polyolefin of the thermoplastic adhesive layer is selected from the group consisting of (1) copolymers of ethylene and at least one first comonomer of unsaturated carboxylic acid or derivative of the acid, (2) olefin polymer grafted with at least one unsaturated carboxylic acid or derivative of the acid, and (3) blends of the copolymers and the grafted olefin polymers. In addition, the copolymer preferably further comprises at least one second comonomer selected from the group consisting of alkyl esters of xcex1, xcex2-ethylenically unsaturated carboxylic acid, vinyl esters of carboxylic acid and carbon monoxide.
The invention also provides for a process for making the laminated film structure. An amine functional polymer is deposited on a fluoropolymer film to form a primed fluoropolymer film. A layer of thermoplastic adhesive comprising acid modified polyolefin is formed on and adhered to the amine functional acrylic polymer of the primed fluoropolymer film. A thermoplastic substrate is formed and adhered to the layer of thermoplastic adhesive. In a preferred form of the invention, the adhesive layer of the laminated film is extruded onto to the primed fluoropolymer film. Most preferably, the adhesive layer and a thermoplastic substrate are coextruded onto the primed fluoropolymer film.